a) Field of the Invention
This invention relates to a stator, which is provided with a one-way clutch and is useful in a torque converter.
b) Description of the Related Art
In FIG. 4, a conventional stator 10 provided with a one-way clutch is shown. In the drawing, numeral 21 indicates an impeller of the stator 10, while numeral 22 designates a radially-inner, cylindrical part of the impeller. On an inner periphery of the radially-inner, cylindrical part 22, a one-way clutch 30 is arranged. Designated at numerals 31,32 are an outer ring and an inner ring of the one-way clutch 30, respectively. The outer and inner rings 31,32 are both rotatably supported on bushes 35. Aluminum alloys have been used primarily as materials of such bushes in order to allow the bushes to exhibit a bearing function. The bushes 35 also serve as bearing tracks for needle bearings 40 disposed on axially-outer sides of the one-way clutch 30, respectively. These bushes 35 are provided with lubrication holes to supply lube oil to the one-way clutch.
FIG. 4 also shows splines 33, via which the inner ring 32 is secured on a central fixing part (not illustrated) of the stator 10, and a central axis Xxe2x80x94X of the stator 10.
In the conventional stator 10 of FIG. 4, each bush 35, as a single-piece part, functions as a bearing for supporting the inner and outer rings 32,31 of the one-way clutch 30, and also as a back-up member for a side plate of the one-way clutch 30 and for the needle bearing 40. Each bush 35 is also provided at its rolling surface for the corresponding needle bearing 40 with oil grooves for cooling the needle bearing. Because each bush 35 is a single-piece part, it is necessary to make the bush with a bearing alloy in its entirety and then to form grooves and ridges by cutting. As a corollary to this, such bushes are relatively expensive. With such a conventional construction as described above, the aluminum-made bushes are required to be dimensioned large in thickness to provide them with strength as high as needed.
As another example, end bearings are used to rotatably support an inner ring and an outer ring of a one-way clutch, and lock plates are employed to support the one-way clutch at side portions thereof via the lock plates, respectively. This example, however, involves a problem in that any attempt to shorten the axial length of the one-way clutch makes it difficult to machine resilient pieces, which are required to produce an outer cage drag, into cages.
To solve the above-described problem, an object of the present invention is to provide at low cost a stator having a reduced dimension in an axial direction by improving bearings of a one-way clutch and support structures for side portions of the one-way clutch.
According to one aspect of the present invention, a stator is provided with an impeller and a one-way clutch arranged in a radially-inner part of the impeller. The stator comprises at least one plain bearing and at least one side plate arranged on an axially outer side of the plain bearing. The plain bearing is arranged adjacent to and on an axially outer side of a side portion of the one-way clutch and between an inner ring and an outer ring of the one-way clutch, and on inner and outer peripheries thereof, having flanges with bearing tracks formed thereon, respectively. The side plate is arranged at a position adjacent to the plain bearing such that the side plate serves not only as a stopper for the plain bearing but also as a bearing track for a needle bearing disposed on an axially-outer side of the side plate. The plain bearing and the side plate are provided with engageable portions, respectively, and are maintained in engagement with each other via the engageable portions.
Preferably, the stator may further comprises an additional plain bearing and side plate as defined above, which are arranged on an axially outer side of an opposite side portion of said one-way clutch such that said additional plain bearing and side plate are maintained in engagement with each other via engageable portions thereof.
Where the plain bearing and side plate are arranged on the axially outer side of only one of the side portions of the one-way clutch, the other side portion of the one-way clutch can be supported by a known method. As disclosed in JP 2001-323985 A, for example, a radially inner, cylindrical part of an impeller can be extended inwardly in a radial direction such that the thus-extended portion, on its inner surface, is maintained in sliding contact with an outer ring and also rotatably supports a side portion of the one-way clutch, and on its outer surface, rotatably supports a needle bearing.
As the stator according to the present invention is constructed as described above, the provision of the plain bearing and the side plate as discrete members and the arrangement of the plain bearing in engagement with its corresponding side plate have made it possible to provide the stator with a reduced dimension in the axial direction. Further, the plain bearing and side plate can be formed at low cost by subjecting plate-shaped blanks to pressing which is an easy machining method. When these plain bearing and side plate are arranged in a form engaged with each other via the engageable portions, they can show performance at least comparable with conventional bearings although the stator is available at low cost.